Flow rate limiters for hydraulic circuits are generally constituted by mechanical shutters whose movement is controlled by a flow rate detector. Now such devices sometimes operate erratically and always require a noticeable response time, which is undesirable for the safety of the installations which they are intended to protect.
For this purpose French Pat. specification No. 2,161,851 (no English language equivalent) describes supercavitation units i.e. having high cavitation, for insertion in hydraulic circuits to limit the flow therethrough. But in most cases the units described do not lend themselves to being inserted in the hydraulic circuit. These units usually require a passage of cross-section which is very much smaller than that of the hydraulic circuit in which the unit is to be inserted, together with a converging portion upstream and a diverging portion downstream. The result is that such a supercavitating unit is very long and is not easily adapted to a hydraulic circuit.
Preferred embodiments of the present invention provide statically operating flow rate limiters for hydraulic circuits which are of small bulk and whose insertion in the hydraulic circuit presents few problems.
The invention provides a flow rate limiter for a hydraulic circuit, comprising means defining a passage whose inside wall is a circular cylinder having an upstream end and a downstream end. A streamlined body is disposed coaxially on the axis of the wall and includes a nose at its upstream end and a tail at its downstream end. Obstacles are disposed in the annular space between the wall and the body, said obstacles causing a supercavitation in the said annular space under the influence of a predetermined flow rate through the passage. Means are provided for fixing the body and the obstacles to the passage defining means.
Preferably the means for fixing the streamlined body are constituted by radial fins supported by the wall.
In that case the obstacles can be supported by a ring disposed in the annular space with the ring fixed to the said radial fins.
In one configuration the obstacles are disposed beside the nose of the streamlined body, the nose itself being disposed at the upstream end of the limiter.
In another configuration the obstacles are disposed beside the tail of the streamlined body, which is itself disposed at the downstream end of the limiter.
An embodiment of the invention is described by way of example with reference to the accompanying drawings.